import requests

xml = """<?xml version="1.0" encoding="ISO-8859-1"?>
     <!DOCTYPE MESSAGE SYSTEM "http://127.0.0.1:80/psms/dtd/messagev12.dtd">
     <MESSAGE VER="1.2">
     <USER USERNAME="xxxxx" PASSWORD="xxxx" />
     <CONTENT  UDH="0" CODING="1" TEXT="SAMPLE" PROPERTY="0" ID="1" TEMPLATE="">
     <ADDRESS FROM="XXXX" TO="XXXXXXXXXX" SEQ="0" TAG="test"/>
     ......
     ......
     </CONTENT>
     </MESSAGE>"""

     payload = {'data'   : xml,'action'   : 'send'}
     headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 6.0; WOW64; rv:24.0) Gecko/20100101 Firefox/24.0',
               'Content-Type': 'application/xml'}
     response =  requests.post(url, params = payload, headers=headers)
     print response.status_code
     print response.content

Traceback (most recent call last):
File "C:UsersdellDesktopSMS XMLxml_sms_api.py", line 30, in <module>
response =  requests.post(url, params = payload, headers=headers)
File "C:Python27libsite-packagesrequestsapi.py", line 110, in post
return request('post', url, data=data, json=json, **kwargs)
File "C:Python27libsite-packagesrequestsapi.py", line 56, in request
return session.request(method=method, url=url, **kwargs)
File "C:Python27libsite-packagesrequestssessions.py", line 488, in request
resp = self.send(prep, **send_kwargs)
File "C:Python27libsite-packagesrequestssessions.py", line 609, in send
r = adapter.send(request, **kwargs)
File "C:Python27libsite-packagesrequestsadapters.py", line 473, in send
raise ConnectionError(err, request=request)
ConnectionError: ('Connection aborted.', BadStatusLine("''",))